It is known for example from Ann. Rev. Plant Physiol. 1979, 30: 105-130 and Ann. Rev. Plant. Physiol. 1984, 35:34-275 that plants utilize a great variety of mechanisms to protect themselves from infections by pathogens. These mechanisms include for example modifications in the cell wall structure, synthesis of toxically acting phytoalexines, accumulation of so-called PR proteins (pathogenesis-related proteins), protease inhibitors and enzymes with hydrolytic functions.
It is further known for example from Biochem. J. 1983, 216:617-625 that various plants can generate proteins which have the ability of inhibiting the ribosomes of eucaryotes. Characteristic of such proteins inhibiting protein synthesis is the property of not influencing the plant-inherent ribosomes whilst they inactivate the plant-foreign ribosomes. Such proteins have become known in particular under the designation "RIP" proteins (ribosome-inhibiting proteins). Of most of these proteins, only their molecular weight and their mode of action are known.
Among the plants in which RIP proteins have been found are the barleys. Thus, in Carlsberg Res. Commun. Vol. 51,1986, p. 129-141, the purified protein, the molecular weight thereof and the amino acid sequence are described.
It is further known, for example from Biochemica et Biophysica Acta 880, 1986, p. 161-170 that RIP proteins are able to inhibit "in vitro" pathogens.